Method of and apparatus for reclaiming spent pickling solution



Apr. 3, 1923. 1,450,217

H. s. MARSH ET Al.

METHOD OF AND APPARATUS FOR RECLAIMING SPENTv PICKLINGSOLUTION H. S. MARSH ET AL 2 sheets-sheet 2 Filed Aug. 5, 1921 Apr. 3, 1923.

METHOD OF AND APPARATUS FOR RECLAIMING SPENT PIGKLING SOLUTION sa ii 'a' divi u. IE e:

WIT/VESSES Patented pr. 3, 1923.

FFE

PATT

HENRY S. MARSH AND RALF S. COCHRAN, 0F YOUNGSTOWN, OHIO.

METHOD OF AND APPARATUS FOR RECLAIMING SPENT PICKLING SOLUTION.

Application :Bled August 3, 1921. Serial No. 489,545.

invented or discovered certain new and use.

ful Improvements in Methods of and Ap aratus for Reclaiming Spent Pickling Soll) tion, of which improvements the following is a specification.

Our invention relates to methods of. and apparatus for the treatment Aof liquids bur-v dened with salts in solution, with the end in view of separating the salt from its solvent. The invention, though not in its broader aspect so limited, finds primary application in the removal from spent pickling solutions used in metal-working mills and factories their burden of metallic salt, and so reclaiming them for repeated service in the pickling operation. The ends in view are economy in the metal-treating operation, and regarding the industry in its relation to the community at large, the rectification and salvage of an undesirable and deleterious by-product. vThe invention constitutes an improvement upon our rior inventions, described and claimed in liietters Patent of the United States, Reissue No. 15,119, granted us originally February 22, 1921, and reissued June 7, 1921, and in a pending ipplication of ours, Serial No. 432,952, filed ecember 24, 1920.

Apparatus in which and in the operation of whlch our present invention will be found, is illustrated in the accompanying drawings. Fig. I is a view in plan from above of apparatus of one particular form'; Fig. II is a view in side elevation of a portion of the .40 apparatus ofFig. I; Fig. III is a diagrammatic showing of another form of apparatus. A s presently will appear, the invention is present in both forms, and other variant forms will readily present themselves to the mind'of the trained engineer.

The method disclosed in our'earlier applications alluded to is a method wherein the spent pickling solution (the substance rimarily in contemplation) is caused to ow in a loopedconductor, the two branches of the loop being in heat-exchanging relation one to the other, a cooling agent is brought to bear upon the iowing stream in the loop of the circuit, and the salt, precipitated by 55 cooling, is allowed to separate by gravity from the stream as it flows. The so sepf arated precipitate is, according to our earlier disclosures withdrawn from the stream, mingled necessarily with an appreciable quantity of the mother liquor, and, according to the disclosure of the later of our two applications above mentioned, the withdrawn material is carried to a centrifuge. In the centrifuge the mother liquor is separated from the salt, and from the centrifuge the separated mother liquor is returned to the flowing stream first mentioned.

According to the method as now improved, there is no initial gravitational separation of precipitated salt from the great body of the flowln stream. To the contrary precipitate and liquid are carried forward together,

under conditions which diminish to the utterm ost the possibllity of gravitational se aratlon, and the whole is introduced into t e centrifuge. From the centrifuge the whole volume of liquid emer es and enters thence the return branch oft e loop. The gain is simplification of apparatus and of operation.

There are incidental features modifying the operation as heretofore disclosed, and these features will become apparent as description proceeds.

Referring first to Fig. I of the drawings, four concentrically arranged spiral coils are shown, bearing consecutively the reference numerals` 1, 2, 3, 4. The fourth .and innermost of these coils is lin Fig. II shown, detached for simplification from the rest, in side elevation. Each coil is double, consisting of two concentrically arranged pipes, and -thus two passageways ,are formed, adapted to carry oppositely flowing streams, separated one from another by tli. walls Off the inner pipe, and thus in lheat-iriterchangl ing relation, one to,t1e.-other. 'The inner ipe is-formed of yacid'esisting material; it 1s continuous, through all thecoils, from the approach 5 to the outermost' coil vto the escape 6 from the innermost. It is preferably formed of seamless co per tubing of .the thinnest stock practicable, andany necessary joints are preferably formed-R y welding. The structure in view is a `nveyor through whose walls heat may pass by conduction most readily, smooth within, and uniform in bore from end to end, in order that the iowing stream may advance in uninterrupted sweep, without swirl or eddy. The outer pipe of each coil must be stron to withstand pressure; it also will be forme .vantageously be formed o material suitably strengthened and rendered water-tight, and acid-resistant, either by lead linlng, glazing, or otherwise.

The outer passageways of the several coils are not connected all of them in lseries as the inner passageways are connected, to form a single continuous conveyor. As shown, the outer passageways of coils 3 and 1 are so connected, thro-ugh the .connecting pipe 7 but the outer passageway of coil 2 is connected at opposite ends with` leads 8 and 9, and the outer passageway of coil 4 1S similarly connected with leads 10 and 11.`

The reclaimed acid (reclaimed in the manner presently to be described) flows through lead 12 and gains access' to the outer passageway of coil 3, after traversing that passageway from end to end, this stream of'reclaimed acid passes through pipe 7 to the outer passageway of coil l, and, traversing that passageway from end to end, enters lead 13,

through which it iows to the pickling vat or to a suitable place of sto-rage.A lThrough the outer passageway of coll 2 a sultable cooling Huid circulates, and, as noted on the drawing, coldl water is a suitable fluid, when the pickling solution from iron or steel pickling is under treatment. Through the outer passageway of coil 4 another cooling fluid circulates. We have noted on the drawing that a suitable cooling fluid here is ammonia, and this it will be understood is the cooling medium of a suitable refrigerating apparatus.

The mechanical unions of inner and outer tubes of the several coils may Yconveniently be made by welding. i

Lead 6 carries the material under treatment to separating apparatus, conveniently a centrifuge; lead 12 brings back reclaimed acid from the apparatus last mentioned.

Operation will readily be understood. Spent pickling solution flowing from' the pickling vat or' from. a place of storage enters at a temperature of 150 F. say, through lead 5, the inner tube of coil 1; traversing that it passes in what is really a continuous conduit throughl the inner tube of each coil, and advances finally through lead 6 to the separating apparatus (not shown in-Fig.- I). Reclaimed acid, returning through lead 12, traverses the outer pipe of coils 3 and 1 successively, and passes on finally through lead 13 to a pickling vat again, or perhaps to a storage tank. Thus it will be seen' that the stream'from vits entrance through lead 5 into the apparatus to `its exit through lead 13 is looped upon itself, and that, as in the disclosures of our earlier specifications the two branches of the loop are arranged in heat-exchanging relative positions.

In the loop (or, to speak more specifically, in the innermost coil 4) the flowing stream is exposed to the cooling effect of the ammo-nia circulating in the outer pipe of this coil This also, so far as method is concerned, presents no departure from our earlier' disclosures. We have, however, so far modified the method of cooling that the entering stream, before reaching the loop of the circuit is exposed, notas in the earlier case continuously tothe cooling effect of the outfiowing streamv of reclaimed acid, but is exposed alternately, first to the cooling effect of the stream of reclaimed, acid, then (in coil 2) to the cooling effect of a circulating stream of cold.` water, then again to the stream of reclaimed acid, at a point higher up in that stream, where the reclaimed acid is cooler, and then at length it reaches the loo of the circuit.

nother difference is to be noted between the apparatus and. methods of our earlier applications and this: In those the precipitated salt was' separated from the stream and sent separately to the centrifuge; here the whole stream goes to the sepa-rating apparatus.

Recurring to the progress of the material through the apparatus, it is to be remarked that, because of the presence of the two bodies of cooling media circulating in the outer pipes of coils 2 and 4 the inflowing stream'is cooled as it advances', and that proportionately as it is cooled the outflowing stream as it traverses coils 3 and l is heated again. The spent acid ente-rs as has been said at a temperature of 1500, more or less. In coil lxit comes into heat-exchanging relation with the outflowing stream of reclaimed acid which reaches coil 1 at a temperature of say 40. In consequence of heat interchange the advancing stream of entering spent acid passes from coil 1 tocoil 2 at a tempe-rature of 800, more or less. In coil 2 the advancing stream is by heat transfer to the cooling medium there circulating reduced still further in tempera-ture, to approximately-,60O- In coil 3 there is further heat'fexchange with the outflowing stream of reclaimed acid, in consequence of which the infie-wing stream is reduced in temperature to approximately 40. The loop of the circuit is nowA reached, and now as the inflowing stream. advances through coil 4 it is by heat interchange with the refrigerating medium there encountered, reduced to approximately 30. From coil 4 the material under treatment fiows to the separating apparatus, and from the separating' apparatus the 'reclaimed acid returns at substan-` tially unchanged temperature to the outer pipe of coil 3. When it reaches coil 3 the loop of the circuit is completed. In coil 3 the outflowing reclaimed acid is warmed from a temperature of yapproximately 30 eov to 40; it Hows-from coil 3 to coil 1, and in coil 1 is further warmed to approximately 130, at which temperature it passes from the apparatus, to enter the pickling vat directly, or perhaps a storage tank.

Returning now to the progress of the material under treatment, it is cooled in its advance through the inner tube of the successive coils from its initial temperature of 150 m-o-re or less gradually to and slightly beyond the freezing point of water. As this point is reached the far greater part of the dissolved copperas is precipitated, and, being precipitated from a flowing stream, it is preci itated in the condition of small and nely ivided crystals. In consequence of the fact that the streamv flows constantly l and uniformly and without pockets or eddies,

the precipitated crystals are swept along to the separating apparatus. In that apparatus the precipitated crystals are removed, and by their removal reclaimed acid remains. This reclaimed acid, returning through'the apparatus takes up heat again.

The heat economies are, with recognition of the modification due to the presence of the cooling medium in coil 2, essentially such as we in our earlier inventions have contemplated. The particular temperatures named 1n' the foregoing description are given in illustrative and exemplary sense; manifestly there may be considerable variation and de parture from the actual figures iven.

The elimina-tion of the step o gravitational separation of the precipitated salt from the iowing stream, before introducing it to the centrifuge or equivalent apparatus, is a simplification; .our perception that the whole body of materialmunder treatment may pass through the centrifuge is an invention that makes for economy.l The refinement of usin a second cooling medium, active on the inflowing branch of the looped stream of'material is a refinement which we find makes for eiiiciency. It will be realized that the temperature of this cooling'medium is variable under the control of the user.

- We have used vthe expressions loop formed course and-loop of the circuit, and shall use'them intheensuing claims. That the course of the flowing stream is loop formed, is manifest that the two branches of the loop are inheat-interchanging relationship, 1s manifest. By the expression the loop of Ithe circuit we mean to designate that portion of the course of the iiowing stream which lies between the exit from the inner pipe of coil 3 to the entrance to the outer pipe of the same coil. That is to say, from point m, Fig. I, to point n. In this interval the stream advances through the inner pipe ofA coil 4, through lead 6, through the separating apparatus, and through lead l12. y,

Fig. III serves to illustrate the 'Lfact that the helical shape and the nesting together in concentric assembly of the several heatexchangin units, are mere matters of convenience. ere, 1n place of four coils, four straight-away lengths of double pipe, 1, 2, 3, and 4a are shown. l Here also are shown diagrammatically, refrigeration apparatus for the. heat-exchanger et,v and a centrifu e. Additionally, a settling tank is indicate ,into which the reclaimed acid may pass from the centriu e and before it begins its return iow; an also a pump is diagrammatically indicated, by means of which circulation may be maintained. In this case, the inflow is indicated to be vitational, and the return to be efecte by the pump; but, as will be perceived, this is a matter of engineering contrivance, and different arrangements will be made under different circumstances. Fig. III shows also a valve-controlled lead 14 from the water supply to the pipe 7 which conveys the returning reclaimed acid 'fromf h'ea1texchanger 3 to la. It is manifest that the removal of the salts, effected in the centrifuge (and copperas contains a large content of water of e stallization), must diminish the volume o the stream, so that, but for augmentation, the outiow must be less than the inliow. Furthermore, in consequence of the addition in the `pickling vat of, fresh acid as the solution continues in service, it does practically come about that the reclaimed acid is often stronger than is required. For such reasons it may be found desirable to introduce water into =.the out flowing stream' in such manner and under such conditions of control as are indicated.

Otherwise than now indicated, the correspondence of the showing'of Fig. III to that of Fig. I will be apparent on comparison, and manifestly, the mode'of operation, wherein lies our invention so far as concerns method, is, with the detail explained, identically the same.

4 We clalm as our inventibn:

1. The method herein described of removing from a solvent its burden of saltwhich consists in causing the solvent, laden iniv-tially vwith the dissolved salt, to iow in a looped circuit, with the branches of the circuit in heat-exchanging relationship one to the other, cooling the liowing stream in the loop of the circuit to a temperature lower than the point of salt precipitation, and causing the entire stream after such cooling and before entering the return branch of the circuit to undergo the operation of a centrifuge. v f

2.. The method herein described of removing from a solvent its burden of salt which consists in causing the solvent, laden initially with the dissolved salt, to iiow in a looped circuit, with the branches of the circuit in heat-exchanging relationship one to the other,wcooling the stream at a point intermediate the length of the iniowing branch of the circuit, coolin the stream a second time in the loop of t e circuit and to a temperature lower than the point of salt precipitation, and after such separate cooling and before the flowing stream enters the return branch of the circuit, separating fromthe stream'the precipitated salt.

3. The method herein described of removing from a solvent its burden of salt which consists in causing the Solvent, laden initially with the dissolved salt, to ow in continuous stream, causing a stream of water in part to fiow in heat-exchanging relation to the flowing stream of solvent at a higher point'in the course thereof, and in part to mingle with the flowing stream of solvent at a lower point in the course thereof, and in separating from the stream of solvent at an intermediate point the burden of salt.

4. The method herein described of reclaiming spent pickling solution which consists in causing the spent solution, while still retaining the heat of the pickling operation, to enter and having entered to flow in. continuous stream and in its entirety through a loop-formed course, the branches of the stream being in heat-exchanging relationship, one to the other, and through a centrifuge arranged in the turn of the course, and in colling the flowing stream on the intake side of the centrifuge to a temperature lower than the point of salt precipitation.

5. In apparatus for unburdening a solvent of its load of salt, a loop-formed conduit, the branches of the loop separated by a wall through which heat may pass from the stream owing in one branch to the stream flowing in the other, a centrifuge in the loop of the circuit into which and from which the entire stream flows, and means for cooling the flowing stream on the inflow side of the centrifuge, substantially as described.

6. In apparatus for unburdening a solvent of its load of salt, a loop formed conduit with branches in heat-exchanging'relation' one to the other, cooling means 'arranged at a point'intermediate the length of the in fiowing branch of the conduit, a second lcooling means arranged in the loop of the conduit, and separating means arranged in the loop of the conduit beyond the cooling means last mentioned, substantially as described.

7 In apparatus for unburdening a solvent of its load of salt the combination of four heat-exchangers each including two liquidconveying elements, four of @gid elements (one element of each of said-h at exchangers) being connected in series and adapted to convey in continuous flow an entering stream of solvent, the second element of the third kand the second element of the first heat-exchanger being connected in series', in the order named, and adapted to convey in continuous ow the escaping stream of solventl` means forv causing a separate cooling medium to circulate in the second element of the second heat-exchanger, means for causing a separate cooling medium to circulate inthe second element of the fourth heat exchanger, and separating apparatus adapted to receive the stream of solvent as it advances from the fourth heat-exchanger and to deliver the solvent again to the third heat-exchanger, substantially as described.

8. In apparatus for unburdening a solvent of its load of salt the combination of a conduit adapted to convey a body of solvent in continuous stream, means for causing a stream of liquid in part to flow over the surface of the said conduit at a higher point in the extent thereof, and in part to enter the said conduit at a vlower point in the extent thereof, and means arranged at an intermediate point for separating salt from the solvent, substantially as described.

` 9. In apparatus for unburdening a solvent I of its load of salt the combination of three heat-exchangers and a centrifuge, each heatexchanger including two elements, three of said elements (one element of each of said heat-exchangers) being connected in series and affording a conduit for the continuous ow of .the solvent and for the delivery of the entire stream to the centrifuge, means for` causing a cooling medium to circulate in the second element of theithird heat-exchanger,

the second element of the second heat-exchanger and the second element of the rst heat-exchanger being connected and affording a conduit for the return How of the solvent issuing from the said centrifuge, substantially as described.

In testimony whereof we have hereunto set our hands.

HENRY S. MARS-H. RALF S. COCHRAN; 

